A heat treatment is applied to a wafer used for manufacturing a semiconductor device. The heat treatment is carried out by placing a vertical wafer boat on which many wafers are mounted in a heat treatment device.
In recent years, the wafer has an increased diameter, so that the wafer is liable to slip. Accordingly, a countermeasure for that is an important problem. As the countermeasure to suppress the slip, for instance, Patent Literature 1 proposes an invention in which the wafer support portion supports from the outer peripheral part of the wafer to the position of 40 to 60% of the radius thereof to minimize a deformation of the wafer and suppress the occurrence of the slip.
A vertical wafer boat disclosed in the Patent Literature 1 will be described below by referring to FIG. 8. FIG. 8 illustrates a state that the vertical wafer boat is seen through from its upper part.
A wafer boat 100 includes support members 101 and 102 in a starting end side seen from a wafer inserting direction X and a support member 103 in a terminal end side, arranged in parallel to each other in a vertical direction. These support members 101, 102 and 103 are allowed to stand upright on a disk shaped base (a bottom plate). Further, upper end parts of the support members are supported by a disk shaped upper fixing member (a top plate).
A circumscribed circle 105 shown in FIG. 8 indicates the upper fixing member (the top plate) of the wafer boat 100. Further, a symbol W shown by a dotted line indicates a mounting position (referred to as a wafer W) of a mounted on the wafer boat 100. Further, an arrow mark X shows an inserting direction of the wafer W to the wafer boat 100.
The support members 101, 102 and 103 respectively include support post parts 101b, 102b and 103b and a plurality of wafer support parts 101a, 102a and 103a respectively horizontally protruding from side surfaces of the support post parts 101b, 102b and 103b and formed to be long.
Further, the support members 101 and 102 located in the wafer insert starting end side are formed to be linearly symmetrical to each other with respect to a dashed-dotted line h that passes through an insertion center point O of the wafer W and extends in the inserting direction X of the wafer W.
Further, the support member 103 located in the wafer insert terminal end side is provided on the dashed-dotted line h that passes through the insertion center point O of the wafer W and extends in the inserting direction X of the wafer W.
Further, the support members 101 and 102 located in the wafer insert starting end side are formed substantially in bent leg shapes in horizontal sections including wafer support parts. On the other hand, the wafer support part 103a is extended substantially linearly from the support member 103.
Here, end parts of the wafer support parts 101a and 102a of the support members 101 and 102 located in the wafer insert starting end side and an end part of the support member 103 located in the wafer insert terminal end side are constituted so as to be located in positions of 40 to 60% of the radius of the wafer W from the outer peripheral part of the wafer.
According to the above-described structure, the wafer W is supported (three point support) by the wafer support parts 101a, 102a and 103a, so that a deformation of the wafer W can be suppressed. As a result, it is possible to expect that a concentration of stress to a specific position of the wafer can be mitigated and a countermeasure for reducing a slip can be made to be effective.